The present invention relates to a molding resin composition, and more particularly relates to a molding resin composition of polyimide which is excellent in high-temperature stability, chemical resistance and mechanical strength as well as processing ability in molding.
Polyimide has so far been excellent in mechanical strength, dimensional stability, high-temperature stability, flame retardance and electrical insulative properties. Therefore polyimide has been used in the field of electric and electronic parts, aeronautics and space instruments and transport machinery. It is also expected for a wide use in the future in the field where high-temperature resistance is required.
A variety of polyimides which exhibit outstanding properties have been developed. Some polyimides, however, have no distinct glass transition temperature, although they are excellent in high-temperature stability. As a result, when employed as molding materials, specific methods such as sinter molding must be used for processing. Other polyimides which are excellent in processability have low glass transition temperatures and are soluble in halogenated hydrocarbons, which renders these polyimides unsatisfactory for use in applications which require high-temperature stability and solvent resistance. Thus, these polyimides have numerous advantages and disadvantages.
Accordingly a polyimide has been desired which is excellent in high-temperature stability and solvent resistance and also has an outstanding processing ability as a molding material.
The present inventors have found a polyimide which satisfies the aforementioned proparties. The polyimide has recurring units of the formula: ##STR2## wherein X is a divalent radical selected from the group consisting of a radical having the formula: ##STR3## and R is a tetravalent radical selected from the group consisting of an aliphatic radical having 2 or more carbon atoms, alicyclic radical, monoaromatic radical, fused polyaromatic radical, and polyaromatic radical where aromatic radicals are linked to one another directly or via a bridge member.
This polyimide is disclosed by Mitsui Toatsu Chemicals, Inc. in Japanese Laid-Open Patent Nos. TOKKAISHO 63-243132 (1988), 64-9226 (1989) and 64-9227 (1989).
The above polyimide is a thermoplastic polyimide having fluidity at high temperatures in addition to excellent mechanical, thermal and electrical properties.
Compared to ordinary engineering polymers represented by polyethylene terephthalate, polybutylene terephthalate, polysulfone and polyphenylene sulfide, polyimide is superior in high-temperature resistance and other properties. On the other hand, the processing ability of the polyimide is still inferior to these polymers.
Generally, in injection molding or extrusion molding, a lower melt viscosity leads to better processing ability. For example, a higher melt viscosity requires a higher injection pressure in the molding stage and the molded products are subject to excessive stress, thereby lowering operation efficiency and causing adverse effects on the properties of the molded products. The above stated polyimide can be injection molded because it has an excellent fluidity at high temperatures. Nevertheless it is desirable to enhance the workability of the polyimide.